1. Field of the Invention
The present invention relates to an assembly of two elements mounted one on the other nonremovably (under normal conditions of use) and free to rotate one with respect to the other. The invention is most specifically aimed at arrangements of two or more elements which, especially because of their low strength in terms of axial compression, could not be fitted together by conventional snap-fitting. This is the case, in particular, when the body of one or the other of the elements consists of a bellows. The invention is particularly adapted to the production of a mixer of the kind used in the field of hair dyeing, although other applications may be envisaged.
This application claims priority of French Patent Application No. 9710819 which is hereby incorporated by reference.
2. Discussion of the Related Art
The irreversible stoppering of containers, containing, for example, samples for medical use, is known. By way of example, mention may be made of U.S. Pat. Nos. 4,736,859, 4,799,597 or 4,934,547, which describe the nonremovable, except by destruction, attachment of a lid of a beaker used for collecting urine.
Elsewhere, in particular, in the field of packaging, it is frequent, when a first part is to be fitted onto a second so that it is free to rotate, for the parts to be fitted together by the so-called snap-fitting technique. This technique consists in providing a snap-fitting bead on the outer wall of one of the parts, the bead being capable of having one or more snap-fitting lips or rings formed on the inner wall of the other part which pass over them. For this technique, axial pressure is exerted on the part that has the lips, which pressure, by elastic deformation of the part that has the lips, causes the lips to pass over the bead.
This technique, although satisfactory for a great many applications, proves entirely unsuitable when one and/or the other of the parts to be assembled is too flexible in terms of compression. This happens because assembly by conventional snap-fitting could lead to irreversible deformation of one and/or the other of the parts due to the axial thrust it requires.
A closure system of the snap-fitting type is also described in U.S. Pat. No. 4,460,100. This document describes a closure device in which the stopper comprises a snap-fitting lip and a snap-fitting bead, which consist of a continuous rib from which there originates a number of ramps oriented respectively so as to come into mutual engagement as the stopper is rotated with respect to the container. One of the problems associated with a design of this kind stems from the fact that, because of the presence of the continuous rib, the ramps of the stopper cease being in engagement with the ramps of the container when the rib of one is positioned over the rib of the other, which in certain cases may require axial pressure to be exerted on the stopper in order to finish the passage of the snap-fitting lip over the snap-fitting bead.
In WO 96/28321, the snap-fitting lip and the snap-fitting bead are produced in the form of one or more helical screw threads extending over the entire periphery of the neck of the bottle, forming an angle with respect to the plane perpendicular to the axis of rotation. The snap-fitting lip can pass over the snap-fitting bead, essentially, only by screwing. This occurs because such screw threads define on the periphery two or more superposed ribs, which can be passed over only by following the thread. Put another way, almost all of the snap-fitting lip passes over the snap-fitting bead in rotation, following the screw thread from its entry to its exit. It is not possible to pass over a significant part of the snap-fitting bead by an axial movement. Such a design entails a substantial angle of rotation in order to achieve such an assembly.